Re: 475 questions


Albert Otten
 

Hi Bruce,

I wonder if you would again read 0 Ohm now. Maybe some caps reformed when you powered the scope up.
The combination of a slightly low +110V and a way too low +105/+160V is strange. The +110V should be pulled down by CR1489.

This 475 seems to be your first scope. Otherwise the advice would be to check the wave forms in stead of only DC measurement. You could still do AC ripple measurements (check that your meters block DC). Normally ripple is in the mV range (except perhaps for +110V). You will probably find some very excessive values.

Albert

On Thu, May 21, 2020 at 09:38 PM, <ciclista41@...> wrote:


Hi Albert,

Thanks for replying! I only used an analog multimeter to take the readings,
and I verified them with another analog, so am confident in the values I got.
However, the value of resistance readings has been called into question,
anyway.

I put together a voltage-limiter (150W incandescent bulb in series with the
hot lead of my wall receptacle, which greatly increased my confidence that
turning the scope on would not do further damage.
So far, so good! With the scope turned on, the filament glows dimly, so I
probably should run a 200W bulb, but I don't have one handy. Knowing that the
scope would run without smoke or pops, I took readings with the voltage
limiter and then plugged directly into the wall, with the latter readings in
parentheses. Yes, a larger bulb is in order!

Checking voltages at the same test points that I got the resistance readings
from, I got:

110 = 87 (91) 83%

50 = 37.5 (40) 80%

15 = 10 (10) 67%

5 = 3.5 (3.8) 76%

-15 = -14.2 (14.5) 97%

-8 = -5.7 (6) 80%

UNREG 50 = 40 (47) 94%

105 = 7.5 (9.5) 9%

The scale intensity seems to work fine, but I get no trace at all. I put my
probe in Ch. 1 and put the negative to chassis ground and positive to the
calibrator, but still got nothing. Pushing the beam finder button didn't help,
either. Same story with Ch. 2.
All indicator lamps on the front seem to be working fine. Fan works fine.
Nothing seems to be getting hot.

Time to start desoldering, I guess.

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